It is known that gas turbines contain the following components: a compressor, for compressing air; a combustion chamber for generating a hot gas by burning fuel in the presence of compressed air, which is produced by the compressor; and a turbine for the depressurization of the hot gas which has been generated in the combustion chamber. It is further known that gas turbines give off unwanted nitrogen oxide (NOx) and carbon monoxide (CO). One factor which is known to influence the emission of NOx is the combustion temperature. The scale of the NOx given off is reduced if the combustion temperature is lowered. However, higher combustion temperatures are desirable in order to achieve a higher efficiency and oxidation of the CO.
Two-stage combustion systems have been developed, which ensure efficient combustion and reduced emissions of NOx. In a two-stage combustion system, diffusion combustion is carried out in the first stage, to produce ignition and stability of the flame. In the second stage, combustion is effected using a premix, to reduce the emissions of NOx.
As shown in FIG. 1, a typical state of the art combustion chamber 10 incorporates an injector housing 6 which has a base 5 for the injector housing. An ignition injector 1 for diffusing the fuel, which has an injection hole 4 for the ignition fuel, passes through the injector housing 6 and is fixed to the base 5 of the injector housing. The main fuel injectors 2 run through the injector housing 6, parallel to the ignition injector 1, and are fixed to the base 5 of the injector housing. The fuel inlets 16 supply the main fuel injectors 2 with fuel. A main combustion zone 9 is formed within the outer cladding 19. A pilot cone 20 projects out from the vicinity of the injection hole 4 for the ignition fuel from the ignition injector 1, and has a flared end 22 adjacent to the main combustion zone 9. The pilot cone 20 has a linear profile 21 which forms a zone 23 for the ignition flame.
The compressed air 101 flows from the compressor 50 between supporting ribs 7 through the main fuel swirlers 8 into the main combustion zone 9. Each of the main fuel swirlers 8 provides numerous swirler vanes 80. The compressed air 12 is forced through a set of vanes 10, which are located within the ignition swirler 11, into the ignition flame zone. Within the pilot cone 20, the compressed air 12 mixes with the ignition fuel 30 and is transported into the ignition flame zone 23, where it burns.
Another burner system is the combustion system based on jet flames. By comparison with spin-stabilized systems, combustion systems based on jet flames offer advantages, in particular from a thermo-acoustic point of view, due to their distributed heat release zones and the lack of spin-induced swirling.
Jet flames are stabilized by mixing in hot recirculating gases. The recirculation zone temperatures necessary for this cannot be guaranteed in gas turbines, in particular in the lower partial-load range, by the known annular arrangement of the jets with a central recirculation zone. Here again, therefore, additional piloting is required, and again consists of a pilot burner and a pilot cone.
Here, the pilot cone is welded onto a mounting insert. Fuel or combustion air is fed to the combustion chamber through this mounting insert, for example by means of suitable passages. During operation, thermal expansions occur. These are the different thermal expansions of the various components, and also by the radial thermal expansion of the pilot cone. However, the permanent welded joint inhibits these thermal expansions, which leads to very high stresses on the cone itself. Due to the stresses occurring operation, the components are damaged, for example by cracking, and must as a result be replaced sooner. Hence the inhibiting of the thermal expansion leads to a reduction in the cyclic service life of the components, in particular the cone.